The immigration reform debate over the past few months has led to various interpretations of what constitutees a pathway to citizenship, especially for undocumented immigrants living in the country now.

Arch conservatives have long argued that a path to citizenship already exists, and that we don't need to revise the immigration system in this respect.

For some immigrants, that's technically true: they could return to their home country and apply for a visa. But it's kind of like saying you can travel from L.A. to New York without a car. It's possible, but it's going to take a lot longer than most people believe is reasonable.

If you've entered the U.S. without inspection (by illegally crossing the border, for example), you may be subject to a three- or 10-year bar, meaning you would need to return to your home country and wait at least that long until you could begin applying for a visa to re-enter the U.S.

Waiting out the 10-year bar doesn't guarantee a visa, either. Even for people with family members in the country -- a viable pathway to legal status -- visa waits can be decades. So you could potentially be talking about a "pathway" that takes as long as 30 to 35 years. For people who don't qualify for existing visa categories (there are few visas for lesser-skilled workers who want to stay in the U.S. long-term, for example), there might be no pathway at all.

2. President Obama

Last month, a draft of the president's immigration plan leaked to the media, giving us an idea of what the commander-in-chief considers a reasonable pathway to citizenship. The president proposed creating a probationary immigration status that the nation's 11 million undocumented immigrants could apply for following the passage of a bill.

You could consider this the first prong in his path to citizenship. Immigrants will be forced to meet certain qualifications -- pay a fine, pass a background check, learn English -- and would then be awarded a status that allows them to live and work in the U.S. legally. The probationary status would last no more than eight years under Obama's plan. After that, immigrants will be able to apply for a green card. Under current law, anyone who is granted a green card can apply for citizenship after waiting five years.

You could consider the special access to a green card the second prong of his pathway. The president's plan, more broadly explained in a January speech, also calls for clearing the existing backlog of visa applications in the legal immigration system. That's meant to ensure that undocumented immigrants using this special pathway would not jump ahead of those already waiting for visas.

A group in the Senate working on immigration reform is considering a similar plan to Obama, but the details have not yet been released by lawmakers.

3. Jeb Bush

Former Florida Gov. Jeb Bush, a popular name in discussions about future presidential candidates, did a great job last week of completely confusing everyone about his beliefs on citizenship. The skinny: Bush said one thing in a new book he was releasing, then another in interviews afterward. But for our purposes, let's look at what he said in the book.

In "Immigration Wars," Bush says that undocumented immigrants should not get citizenship at all. Instead, he proposes a path to permanent legal status, but not citizenship. As it stands now, green card holders are able to apply for citizenship after five years. But in the book, Bush lays out a plan that would create a new type of permanent legal status that would not lead to "the cherished fruits of citizenship." The plan would effectively create a second-class of citizenship -- someone with the ability to stay in the country permanently but without the full rights of a citizen.

In interviews earlier this month, Bush said that he's open to citizenship for undocumented immigrants, contradicting the stance in the book.

4. Rand Paul

The Republican senator from Kentucky, and potential presidential candidate, got people talking on Tuesday when early news reports said he was backing a path to citizenship. A few hours later, his stance wasn't so clear.

According to a speech Paul made Tuesday morning, he said that he supports the creation of a probationary status for undocumented immigrants, something similar to the first prong of Obama's pathway. Immigrants who qualify for such a visa would be able to live and work in the U.S., but would not have any special pathway to citizenship, as they would under the second prong of the Obama plan.

"They would get into the back of the line and get no special privileges to do so," a Paul adviser told the Washington Post. "What his plan is extending to them is a quicker path to normalization, not citizenship, and being able to stay, work and pay taxes legally."

Unlike Bush, Paul did not say that his plan would specifically bar undocumented immigrants from seeking citizenship. But if Congress were to create a probationary visa, as Paul proposes, it would also need to decide if such a visa would be eligible for a move to permanent residency or not. For example, guest worker programs are temporary by nature, and don't offer a path to citizenship. Paul hasn't made it clear whether his proposed visa would be more like a guest-worker program, or a visa where the person might be eligible to obtain permanent residency over time.

UPDATE, 5:10 p.m.

Sen. Rand Paul has clarified his stance on a path to citizenship for undocumented immigrants. Apparently he's leery of the phrase "path to citizenship," but not the actual idea. Read about it here.